COS(α-β); SIN α= 1/3, α IN QUADRANT II, TAN β= 4/3, β IN QUADRANT III.

Question

Can someone please show me how to find the exact value and the appropriate identity?

Answer 1

Use the Pythagorean theorem to compute the other needed trig functions

cos alpha = -(2/3)√2

sin beta = -4/5 and cos beta = -3/5

Then use the addition formula to compute required cos.

Be careful with signs!!